When providing flow restrictions in flow systems it is most often desirable to ensure that the obtained flow resistivity is precise and at a desired value, since this adds to the reliability of the flow system. In microfluidic systems it is very difficult to provide flow restrictions having a precise and reliable flow resistivity, since the small dimensions of microfluidic systems increases the requirements to the manufacturing tolerances of the flow restrictions. Accordingly, it is difficult to repeatedly manufacture flow restrictions having resistivities within the same narrow limited tolerances.
An accurate flow resistivity is very desirable in flow systems where the flow rates are only allowed to vary within narrow tolerances, e.g. in flow systems which are used in health care applications, where trustworthy flow rates may be essential. Health care applications may include infusion or monitoring systems based on the principle of mixing reagents to a test sample in order to provide some detectable reaction corresponding to the parameter being monitored, such as the concentration of substances.